Medical imaging systems may use nuclear materials, called radiopharmaceuticals, for the imaging. One such imaging system is single photon emission computed tomography, abbreviated as SPECT. Other medical imaging techniques may include positron emission tomography (“PET”) as well as magnetic resonance imaging.
SPECT imaging attempts to produce a three-dimensional reconstruction of the intensity of the three-dimensional distribution of a photon emitter within the body of the subject being imaged. Typically the emitted photons are gamma-rays from the radiopharmaceutical. SPECT operates by back projecting multiple projection images acquired at equal angular increments over at least 180° around the subject. One or more detector heads collect these projection images and produce a two-dimensional image of the emitted gamma rays.
Having multiple detector heads may increase the camera system's efficiency. This increased efficiency can either be used to improve image quality or to reduce the time of the procedure.
The physical size of imaging heads on current multi-head SPECT cameras has typically limited the camera to have four heads that are positioned over 360°. For a four-headed system, the heads have been typically spaced at 90° increments. One limiting factor is the size of the heads. The head size may constrain the minimum orbit radius, which is the distance from the center of rotation to the photon-sensitive face of the detector heads, for such systems to be approximately 25 cm.
In addition, large heads arrayed over 360° may reduce the ability for patient ingress and egress from the imaging system. The patient enters the imaging volume by being translated into the imaging volume along the axis-of-rotation of the heads.